Quantum dots, a composition or composite including the same, and an electronic device including the same

ABSTRACT

A cadmium free quantum dot including a semiconductor nanocrystal core and a semiconductor nanocrystal shell disposed on the core, wherein the quantum dot does not include cadmium and includes indium and zinc, the quantum dot has a maximum photoluminescence peak in a red light wavelength region, a full width at half maximum (FWHM) of the maximum photoluminescence peak is less than or equal to about 40 nanometers (nm), an ultraviolet-visible (UV-Vis) absorption spectrum of the quantum dot includes a valley between about 450 nm to a center wavelength of a first absorption peak, and a valley depth (VD) defined by the following equation is greater than or equal to about 0.2, a quantum dot polymer composite including the same, and a display device including the quantum dot-polymer composite:(Absfirst−Absvalley)/Absfirst=VD.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 16/817,902, filed on Mar. 13, 2020, which iscontinuation application of U.S. patent application Ser. No. 16/245,728,filed on Jan. 11, 2019, now U.S. Pat. No. 10,590,340, which claimspriority to and the benefit of Korean Patent Application No.10-2018-0003832 filed in the Korean Intellectual Property Office on Jan.11, 2018, and all the benefits accruing therefrom under 35 U.S.C. § 119,the entire contents of which in their entirety are incorporated hereinby reference.

BACKGROUND 1. Field

Quantum dots, compositions, or composites including the same, andelectronic devices (e.g., display devices) including the same aredisclosed.

2. Description of the Related Art

Quantum dots (i.e., nano-sized semiconductor nanocrystals) may havedifferent energy bandgaps by controlling sizes and compositions ofnanocrystals, and thus may emit light of various photoluminescencewavelengths. Quantum dots may exhibit electroluminescent andphotoluminescence properties. In a chemical wet process, organicmaterials such as ligands, dispersing agents or solvents are coordinatedon, e.g., bound to, the surface of the semiconductor nanocrystal duringa crystal growth to provide quantum dots having controlled sizes andphotoluminescence characteristics. Photoluminescence properties ofquantum dots may be applied in various fields. In terms of anenvironmental standpoint, developments for cadmium free quantum dotscapable of providing improved photoluminescence properties aredesirable.

SUMMARY

An embodiment provides a cadmium free quantum dot having improvedphotoluminescence properties.

An embodiment provides a method of producing the cadmium free quantumdot.

An embodiment provides a composition including the cadmium free quantumdot.

An embodiment provides a quantum dot-polymer composite including thecadmium free quantum dot.

An embodiment provides an electronic device (e.g., a display device)including the quantum dot-polymer composite.

In an embodiment, a cadmium free quantum dot includes a semiconductornanocrystal core and a semiconductor nanocrystal shell disposed on thecore and does not include cadmium, wherein the quantum dot includesindium and zinc and has a maximum photoluminescence peak in a red lightwavelength region, a full width at half maximum (FWHM) of the maximumphotoluminescence peak is less than or equal to about 40 nanometers(nm), an ultraviolet-visible (UV-Vis) absorption spectrum of the quantumdot includes a valley between about 450 nm and a first absorption peakwavelength, and a valley depth (VD) defined by the following equation isgreater than or equal to about 0.2:

(Abs_(first)−Abs_(valley))/Abs_(first)=VD

wherein, Abs_(first) is an absorption intensity at the first absorptionpeak wavelength and Abs_(valley) is an absorption intensity at a lowestpoint of the valley.

The red light wavelength region may be in a range of greater than orequal to about 600 nm and less than or equal to about 650 nm.

The full width at half maximum (FWHM) of the maximum photoluminescencepeak may be less than or equal to about 39 nm.

The FWHM of the maximum photoluminescence peak may be less than or equalto about 38 nm.

The FWHM of the maximum photoluminescence peak may be less than or equalto about 37 nm.

The half width at half maximum (HWHM) of the first absorption peak maybe less than or equal to about 25 nm.

A quantum efficiency (quantum yield) of the cadmium free quantum dot maybe greater than or equal to about 80%. A quantum efficiency of thecadmium free quantum dot may be greater than or equal to about 85%. AQuantum efficiency of the cadmium free quantum dot may be greater thanor equal to about 88%.

The cadmium free quantum dot may have a mole ratio of the zinc to theindium that is greater than or equal to about 10:1 and less than orequal to about 40:1.

The cadmium free quantum dot may have a size of greater than or equal toabout 6 nm.

The cadmium free quantum dot may have a mole ratio of the zinc to theindium of greater than or equal to about 12:1 and less than or equal toabout 30:1 and a size of greater than or equal to about 7 nm.

The semiconductor nanocrystal core may include a Group III-V compound.The Group III-V compound may include indium as a Group III metal.

The semiconductor nanocrystal core may not include zinc.

The semiconductor nanocrystal core may have a size of greater than orequal to about 2.5 nm.

The shell may include a first semiconductor nanocrystal shell includingzinc and selenium and a second semiconductor nanocrystal shell disposedon the first semiconductor nanocrystal shell, the second semiconductornanocrystal shell including zinc and sulfur.

The first semiconductor nanocrystal shell may be disposed directly onthe surface of the semiconductor nanocrystal core. The firstsemiconductor nanocrystal shell may not include sulfur.

The first semiconductor nanocrystal shell may have a thickness ofgreater than or equal to about 3 monolayers.

The first semiconductor nanocrystal shell may have a thickness of lessthan or equal to about 10 monolayers.

The second semiconductor nanocrystal shell may be an outermost layer ofthe quantum dot.

The second semiconductor nanocrystal shell may be disposed directly onthe first semiconductor nanocrystal shell.

The second semiconductor nanocrystal shell may include ZnSeS, ZnS, or acombination thereof.

In the quantum dot, a ratio of a total mole amount of sulfur andselenium to a mole amount of indium [(S+Se)/In] may be greater than orequal to about 10:1, for example, greater than or equal to about 11:1and less than or equal to about 40:1, for example less than or equal toabout 30:1, less than or equal to about 20, or less than or equal toabout 15.

The cadmium free quantum dot may have a molar ratio of selenium tosulfur of greater than or equal to about 1:1, for example, greater thanor equal to about 1.1:1. The cadmium free quantum dot may have a molarratio of selenium to sulfur of less than or equal to about 3:1, forexample less than or equal to about 2.8:1.

A thickness of the semiconductor nanocrystal shell may be greater thanabout 1.5 nm, for example, greater than or equal to about 2 nm, orgreater than about 2 nm.

In an embodiment, a quantum dot polymer composite includes a polymermatrix; and a plurality of quantum dots dispersed in the polymer matrix,wherein the plurality of quantum dots includes the aforementionedcadmium free quantum dots.

The polymer matrix may include a cross-linked polymer, a binder polymerincluding a carboxylic acid group, or a combination thereof.

The cross-linked polymer may include a polymerization product of aphotopolymerizable monomer including a carbon-carbon double bond, apolymerization product of the photopolymerizable monomer and a multiplethiol compound having at least two thiol groups (e.g., at a terminal endof the multiple thiol compound), or a combination thereof.

The quantum dot polymer composite may include a metal oxide fineparticle in the polymer matrix.

In an embodiment, a display device includes a light source and a lightemitting element (e.g., a photoluminescent element), wherein the lightemitting element includes the aforementioned quantum dot-polymercomposite and the light source is configured to provide the lightemitting element with incident light.

The incident light may have a photoluminescence peak wavelength of about440 nm to about 460 nm.

The light emitting element may include a sheet of the quantum dotpolymer composite.

The display device may further include a liquid crystal panel, and

the sheet of the quantum dot polymer composite may be disposed betweenthe light source and the liquid crystal panel.

The light emitting element may include a stacked structure including asubstrate and a light emitting layer (e.g., a photoluminescent layer)disposed on the substrate, wherein the light emitting layer includes apattern of the quantum dot polymer composite and the pattern includes atleast one repeating section configured to emit light at a predeterminedwavelength.

The display device may be configured to have color reproducibility ofgreater than or equal to about 80% measured in accordance with a BT2020standard.

The pattern may include a first section configured to emit a first lightand a second section configured to emit a second light having adifferent center wavelength from the first light.

The light source may include a plurality of light emitting unitscorresponding to each of the first section and the second section,wherein the light-emitting units may include a first electrode and asecond electrode facing each other and an electroluminescence layerdisposed between the first electrode and the second electrode.

The display device may further include a lower substrate, a polarizerdisposed under the lower substrate, and a liquid crystal layer disposedbetween the stacked structure and the lower substrate, wherein thestacked structure is disposed so that the light emitting layer faces theliquid crystal layer.

The display device may further include a polarizer between the liquidcrystal layer and the light emitting layer.

The light source may include a light emitting diode (LED) and optionallya light guide panel (LGP).

An embodiment provides a cadmium free quantum dot including

a semiconductor nanocrystal core comprising InP, InAs, or a combinationthereof; and

a semiconductor nanocrystal shell comprising ZnSe, ZnSeS, ZnS, or acombination thereof disposed on the core,

wherein the quantum dot has a maximum photoluminescence peak in a redlight wavelength region of greater than or equal to about 600 nanometersand less than or equal to about 650 nanometers,

a full width at half maximum of the maximum photoluminescence peak isless than or equal to about 37 nanometers, and

a half width at half maximum of the first absorption peak is less thanor equal to about 25 nanometers.

The cadmium free quantum dot according to an embodiment may emit redlight having a relatively narrow full width at half maximum (FWHM) aswell as improved luminous efficiency. The composition including thecadmium free quantum dot according to an embodiment may provide improvedprocess stability. The cadmium free quantum dot may be used in variousdisplay devices and biological labelling (e.g., bio sensor, bio imaging,etc.), a photo detector, a solar cell, a hybrid composite, and the like.A display device including the cadmium free quantum dot according to anembodiment may provide improved display quality (increased colorreproducibility under the next generation color standard BT2020reference).

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 shows a valley depth of a UV-Vis absorption spectrum of a quantumdot according to an embodiment.

FIG. 2 shows a half width at half maximum (HWHM) of a first absorptionpeak in a UV-Vis absorption spectrum of quantum dot according to anembodiment.

FIG. 3 is an exploded view of a display device according to anembodiment.

FIG. 4 shows a process of producing a quantum dot polymer compositepattern using a composition according to an embodiment.

FIG. 5A is a schematic cross-sectional view of a display deviceaccording to an embodiment.

FIG. 5B is a schematic cross-sectional view of a display deviceaccording to an embodiment.

FIG. 6 is a schematic cross-sectional view of a display device accordingto an embodiment.

DETAILED DESCRIPTION

Advantages and characteristics of this disclosure, and a method forachieving the same, will become evident referring to the followingexample embodiments together with the drawings attached hereto. However,the embodiments should not be construed as being limited to theembodiments set forth herein. If not defined otherwise, all terms(including technical and scientific terms) in the specification may bedefined as commonly understood by one skilled in the art. The termsdefined in a generally-used dictionary may not be interpreted ideally orexaggeratedly unless clearly defined. In addition, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.

Further, the singular includes the plural unless mentioned otherwise.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification.

It will be understood that when an element such as a layer, film,region, or substrate is referred to as being “on” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±10% or 5% of the stated value.

It will be understood that, although the terms “first,” “second,”“third” etc. may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer, orsection. Thus, “a first element,” “component,” “region,” “layer,” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

As used herein, when a definition is not otherwise provided,“substituted” may refer to replacement of hydrogen of a compound or agroup by a substituent selected from a C1 to C30 alkyl group, a C2 toC30 alkenyl group, a C2 to C30 alkynyl group, a C6 to C30 aryl group, aC7 to C30 alkylaryl group, a C1 to C30 alkoxy group, a C1 to C30heteroalkyl group, a C3 to C30 heteroalkylaryl group, a C3 to C30cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C30cycloalkynyl group, a C2 to C30 heterocycloalkyl group, a halogen (—F,—Cl, —Br, or —I), a hydroxy group (—OH), a nitro group (—NO₂), a cyanogroup (—CN), an amino group (—NRR′ wherein R and R′ are independentlyhydrogen or a C1 to C6 alkyl group), an azido group (—N₃), an amidinogroup (—C(═NH)NH₂), a hydrazino group (—NHNH₂), a hydrazono group(═N(NH₂)), an aldehyde group (—O(═O)H), a carbamoyl group (—C(O)NH₂), athiol group (—SH), an ester group (—C(═O)OR, wherein R is a C1 to C6alkyl group or a C6 to C12 aryl group), a carboxyl group (—COOH) or asalt thereof (—C(═O)OM, wherein M is an organic or inorganic cation), asulfonic acid group (—SO₃H) or a salt thereof (—SO₃M, wherein M is anorganic or inorganic cation), a phosphoric acid group (—PO₃H₂) or a saltthereof (—PO₃MH or —PO₃M₂, wherein M is an organic or inorganic cation),or a combination thereof.

As used herein, unless a definition is otherwise provided, the term“hetero” means that the compound or group includes at least one (e.g.,one to three) heteroatom(s), wherein the heteroatom(s) is eachindependently N, O, S, Si, P, or a combination thereof.

As used herein, unless a definition is otherwise provided, the term“aliphatic hydrocarbon group” refers to a C1 to C30 linear or branchedalkyl group, C2 to C30 linear or branched alkenyl group, and C2 to C30linear or branched alkynyl group, the term “aromatic hydrocarbon group”refers to a C6 to C30 aryl group or a C2 to C30 heteroaryl group, andthe term “alicyclic hydrocarbon group” refers to a C3 to C30 cycloalkylgroup, a C3 to C30 cycloalkenyl group, and a C3 to C30 cycloalkynylgroup.

As used herein, unless a definition is otherwise provided, the term“(meth)acrylate” refers to acrylate and/or methacrylate. The(meth)acrylate may include a (C1 to C10 alkyl)acrylate and/or a (C1 toC10 alkyl)methacrylate.

In some embodiments, “hydrophobic moiety” may refer to a moietyproviding the corresponding compound with a tendency to be agglomeratedin an aqueous solution and to repel water. For example, the hydrophobicmoiety may include an aliphatic hydrocarbon group having a carbon numberof 1 or greater (e.g., 2 or greater, 3 or greater, 4 or greater, or 5 orgreater) (alkyl, alkenyl, alkynyl, etc.), an aromatic hydrocarbon grouphaving a carbon number of 6 or greater (phenyl, naphthyl, aralkyl group,etc.), or an alicyclic hydrocarbon group having a carbon number of 5 orgreater (cyclohexyl, norbornene, norbornane, tricyclodecane, etc.).

As used herein, “dispersion” may refer to dispersion wherein a dispersedphase is a solid and a continuous phase includes a liquid. For example,“dispersion” may refer to a colloidal dispersion wherein the dispersedphase has a dimension of greater than or equal to about 1 nm, forexample, greater than or equal to about 2 nm, greater than or equal toabout 3 nm, or greater than or equal to about 4 nm and severalmicrometers (μm) or less, (e.g., about 2 μm or less or about 1 μm orless).

As used herein, the term “group” may refer to a group of Periodic Table.As used herein, “Group I” may refer to Group IA and Group IB, andexamples may include Li, Na, K, Rb, and Cs, but are not limited thereto.

As used herein, “Group II” may refer to Group IIA and Group IIB, andexamples of Group II metal may be Cd, Zn, Hg, and Mg, but are notlimited thereto.

As used herein, “Group III” may refer to Group IIIA and Group IIIB, andexamples of Group III metal may be Al, In, Ga, and TI, but are notlimited thereto.

As used herein, “Group IV” may refer to Group IVA and Group IVB, andexamples of a Group IV metal may be Si, Ge, and Sn, but are not limitedthereto. As used herein, the term “metal” may include a semi-metal suchas Si.

As used herein, “Group V” may refer to Group VA, and examples mayinclude nitrogen, phosphorus, arsenic, antimony, and bismuth, but arenot limited thereto.

As used herein, “Group VI” may refer to Group VIA, and examples mayinclude sulfur, selenium, and tellurium, but are not limited thereto.

A semiconductor nanocrystal particle (also known as a quantum dot) is anano-sized crystalline material. The semiconductor nanocrystal particlemay have a large surface area per a unit volume due to a relativelysmall size of the semiconductor nanocrystal particle and may exhibitdifferent characteristics from bulk materials having the samecomposition due to a quantum confinement effect. Quantum dots may absorblight from an excitation source to be excited, and may emit energycorresponding to an energy bandgap of the quantum dots. Quantum dotshave a potential applicability to various devices (e.g., an electronicdevice) due to unique photoluminescence characteristics. Quantum dotshave properties that may be applicable to an electronic device and thelike may be cadmium-based. However, cadmium may cause a seriousenvironment/health problem and thus is a restricted element. As a typeof cadmium free quantum dot, a Group III-V-based nanocrystal has beenextensively researched. However, a cadmium free quantum dot may havepoor photoluminescence properties (e.g., a full width at half maximum(FWHM) and luminous efficiency) compared with those of a cadmium-basedquantum dot. Photoluminescence properties of the cadmium free quantumdot may substantially deteriorate, especially when subjected to variousprocesses for application as an electronic device.

A cadmium free quantum dot according to an embodiment includes asemiconductor nanocrystal core and a semiconductor nanocrystal shelldisposed on the core and does not include cadmium. The quantum dotincludes indium and zinc, the quantum dot has a maximumphotoluminescence peak in a red light wavelength region, a full width athalf maximum (FWHM) of the maximum photoluminescence peak is less thanor equal to about 40 nm, a UV-Vis absorption spectrum of the quantum dothas a valley portion between about 450 nm and a first absorption peakwavelength, and a valley depth (VD) defined by the following equation isgreater than or equal to about 0.2:

(Abs_(first)−Abs_(valley))/Abs_(first)=VD

wherein, Abs_(first) is an absorption intensity at the first absorptionpeak wavelength and Abs_(valley) is an absorption intensity at thelowest point of the valley portion.

As used herein, the term “first absorption peak wavelength” refers to awavelength of a main excitonic peak appearing first from the longestwavelength region of a UV-vis absorption spectrum of a quantum dot(i.e., appearing in the lowest energy region in the UV-Vis absorptionspectrum).

The red light wavelength region may be greater than or equal to about600 nm, for example, greater than or equal to about 605 nm, or greaterthan or equal to about 610 nm. The red light wavelength region may beless than or equal to about 650 nm, for example, less than or equal toabout 645 nm, less than or equal to about 640 nm, less than or equal toabout 635 nm, or less than or equal to about 630 nm. The firstabsorption peak may be present in a range of greater than or equal toabout 580 nm, greater than or equal to about 590 nm, or greater than orequal to about 600 nm, greater than or equal to about 610 nm and lessthan or equal to about 650 nm, less than or equal to about 630 nm, lessthan or equal to about 620 nm, less than or equal to about 610 nm, orless than or equal to about 605 nm.

As used herein, the valley portion of the UV-Vis absorption spectrumrefers to a portion 2 where a slope of a tangent line of a UV-Visabsorption spectrum curve changes from a negative value to a positivevalue, as a wavelength increases. The valley portion may exist near thefirst absorption peak 1 (see FIG. 1).

The cadmium free quantum dot (e.g., a Group III-V compound-based quantumdot including indium (In) and phosphorus (P)) has a smaller bandgap buta larger Bohr radius than a cadmium-based core such as a CdSe core andthe like and thus has a large change of a full width at half maximum(FWHM) depending on a size. In addition, the core including indium andphosphorus (P) is weak about a surface oxidation, e.g., the surface maybe relatively easily oxidized, and thus desired quantum efficiency andfull width at half maximum (FWHM) may not be realized, e.g., provided,after the shell coating. A red light emitting cadmium free quantum dot(e.g., a quantum dot including indium and phosphorus) has a relativelylarge core size (e.g., compared with that of a green light emittingcadmium free quantum dot). The increased core size may cause nonuniformity in a quantum dot size distribution. In addition, the redlight emitting InP-based quantum dot maintains a relatively thin shellthickness for uniform shell coating, which may restrict an increase ofluminous efficiency and a decrease of a full width at half maximum(FWHM). For example, the red light emitting InP-based quantum dot mayhave less than or equal to about 60% of luminous efficiency and greaterthan about 40 nm of a full width at half maximum (FWHM).

The quantum dot according to an embodiment has a large intensitydifference between a first absorption peak and a valley portion adjacentto the first absorption peak in the UV-Vis absorption spectrum. Thevalley depth of the quantum dot according to an embodiment may begreater than or equal to about 0.2, for example, greater than or equalto about 0.21, greater than or equal to about 0.22, greater than orequal to about 0.24, greater than or equal to about 0.25, greater thanor equal to about 0.26, greater than or equal to about 0.27, greaterthan or equal to about 0.28, greater than or equal to about 0.29,greater than or equal to about 0.30, greater than or equal to about0.31, greater than or equal to about 0.32, greater than or equal toabout 0.33, greater than or equal to about 0.34, or greater than orequal to about 0.35.

The quantum dot according to an embodiment may have HWHM of less thanabout 25 nm, for example, less than or equal to about 24 nm, or lessthan or equal to about 23 nm in a UV-Vis absorption spectrum.

The present inventors have found that a valley depth or a half width athalf maximum (hereinafter, HWHM) in a UV-Vis absorption spectrum of thequantum dot has a correlation with a FWHM of a maximum photoluminescencepeak of a quantum dot. As used herein, the term “half width at halfmaximum” refers to a right half width of a UV-vis absorption peakmeasured from the first absorption peak wavelength 1 to a point 2 on theabsorption intensity axis (i.e., y-axis) which is half the maximumamplitude in a lower energy (a longer wavelength) region. (see FIG. 2)

Without being bound by any theory, it is believed that the valley depthmay represent size uniformity of a quantum dot (or a core) or shellcoating uniformity of a core-shell quantum dot. Without wishing to bebound by any theory, the greater the valley depth, the higher the sizeuniformity of a quantum dot (or a core) or shell coating uniformity of acore-shell quantum dot is. The quantum dot according to an embodimentmay have a full width at half maximum (FWHM) of less than about 41 nm,for example, less than or equal to about 40 nm, less than or equal toabout 39 nm, less than or equal to about 38 nm, or less than or equal toabout 37 nm.

In an embodiment, the semiconductor nanocrystal core may include a GroupIII-V compound. For example, the semiconductor nanocrystal core mayinclude indium. The semiconductor nanocrystal core may includephosphorus. The semiconductor nanocrystal core may include InP, InAs,InPAs, GaP, GaAs, InGaP, InGaAs, InGaPAs, or a combination thereof. Thesemiconductor nanocrystal core may not include zinc, i.e., may be freeof zinc or have no zinc added.

The size of the core may be desirably selected considering aphotoluminescence wavelength. For example, the size of the core may begreater than or equal to about 2.5 nm, greater than or equal to about2.6 nm, greater than or equal to about 2.7 nm, greater than or equal toabout 2.8 nm, or greater than or equal to about 2.9 nm. For example, thesize of the core may be less than or equal to about 4.5 nm, for exampleless than or equal to about 4 nm, or less than or equal to about 3.5 nm.

The shell may include a first semiconductor nanocrystal shell includingzinc and selenium. The shell may further include the secondsemiconductor nanocrystal shell including zinc and sulfur and beingdisposed on the first semiconductor nanocrystal shell. In an embodiment,the quantum dot may include a core including indium phosphide (e.g.,InP). The quantum dot may have a core-multi-layered shell structure. Forexample, the quantum dot may include a first shell directly on the coreand including ZnSe, ZnSeS, or a combination thereof. The quantum dot mayhave a core-multi-layered shell structure having a second shell directlyon the first shell, having a different composition from the first shell,and including ZnS, ZnSeS, or a combination thereof.

The cadmium free quantum dot may have a mole ratio of the zinc relativeto the indium of greater than or equal to about 10:1. The quantum dotaccording to an embodiment includes a coating (a shell) having improvedquality and an increased thickness on a core, and the mole ratio of thezinc relative to the indium may represent these characteristics. In thecadmium free quantum dot, the mole ratio of the zinc relative to theindium may be greater than or equal to about 10.5:1, greater than orequal to about 11:1, greater than or equal to about 11.5:1, greater thanor equal to about 12:1, or greater than or equal to about 12.5:1. In thecadmium free quantum dot, the mole ratio of the zinc relative to theindium may be less than or equal to about 40:1, for example, less thanor equal to about 35:1, less than or equal to about 30:1, less than orequal to about 25:1, less than or equal to about 24:1, less than orequal to about 23:1, less than or equal to about 22:1, less than orequal to about 21:1, less than or equal to about 20:1, or less than orequal to about 19.5:1.

The first semiconductor nanocrystal shell may include ZnSe. The firstsemiconductor nanocrystal shell may not include sulfur (S), e.g., may befree of S or have no S added. For example, the first semiconductornanocrystal shell may not include, e.g., may be free of, ZnSeS. Thefirst semiconductor nanocrystal shell may be disposed directly on thesemiconductor nanocrystal core. The first semiconductor nanocrystalshell may have a thickness of greater than or equal to about 3monolayers (ML), or greater than or equal to about 4 ML. The firstsemiconductor nanocrystal shell may have a thickness of less than orequal to about 10 ML, for example, less than or equal to about 9 ML,less than or equal to about 8 ML, or less than or equal to about 7 ML.

In the quantum dot according to an embodiment, a mole ratio of seleniumwith respect to indium may be greater than or equal to about 5.7:1, forexample, greater than or equal to about 5.8:1, greater than or equal toabout 5.9:1, greater than or equal to about 6.0:1, greater than or equalto about 6.1:1, greater than or equal to about 6.2:1, greater than orequal to about 6.3:1, greater than or equal to about 6.4:1, greater thanor equal to about 6.5:1, greater than or equal to about 6.6:1, orgreater than or equal to about 6.7:1. In the quantum dot according to anembodiment, a mole ratio of selenium with respect to indium may be lessthan or equal to about 20:1, less than or equal to about 19:1, less thanor equal to about 18:1, less than or equal to about 17:1, less than orequal to about 16:1, less than or equal to about 15:1, less than orequal to about 14:1, less than or equal to about 13:1, less than orequal to about 12:1, less than or equal to about 11:1, or less than orequal to about 10:1. Without being bound by any theory, the quantum dotaccording to an embodiment includes a first semiconductor nanocrystalshell having a relatively increased thickness, and this shell maycontribute to accomplishing shell uniformity and improving opticalproperties (a valley depth, HWHM, a full width at half maximum (FWHM),and the like) of the quantum dot.

The second semiconductor nanocrystal shell may be an outermost layer ofthe quantum dot. The second semiconductor nanocrystal shell may bedisposed directly on the first semiconductor nanocrystal shell. Thesecond semiconductor nanocrystal shell may include ZnSeS, ZnS, or acombination thereof. In the quantum dot according to an embodiment, amolar amount ratio of sulfur with respect to indium may be greater thanor equal to about 2:1, for example, greater than or equal to about 3:1,greater than or equal to about 3.1:1, greater than or equal to about3.2:1, greater than or equal to about 3.4:1, greater than or equal toabout 4:1, or greater than or equal to about 5:1. In the quantum dotaccording to an embodiment, a mole ratio of sulfur with respect toindium may be less than or equal to about 20:1, less than or equal toabout 19:1, less than or equal to about 18:1, less than or equal toabout 17:1, less than or equal to about 16:1, less than or equal toabout 15:1, less than or equal to about 14:1, less than or equal toabout 13:1, less than or equal to about 12:1, less than or equal toabout 11:1, or less than or equal to about 10:1. In the quantum dotaccording to an embodiment, a mole ratio of selenium with respect sulfurmay be greater than or equal to about 1:1, for example, greater than orequal to about 1.1:1, greater than or equal to about 1.2:1, greater thanor equal to about 1.3:1, or greater than or equal to about 1.4:1. In thequantum dot according to an embodiment, a mole ratio of selenium withrespect to sulfur may be less than or equal to about 5:1, for example,less than or equal to about 4:1, less than or equal to about 3.5:1, orless than or equal to about 3:1. The cadmium free quantum dot having theshell of the composition may exhibit improved optical properties (valleydepth, HWHM, full width at half maximum (FWHM), etc.).

In the cadmium free quantum dot, a mole ratio of a sum of selenium andsulfur with respect to indium (i.e., (S+Se):In) may be greater than orequal to about 3:1, greater than or equal to about 4:1, greater than orequal to about 5:1, greater than or equal to about 6:1, greater than orequal to about 7:1, greater than or equal to about 8:1, greater than orequal to about 9:1, greater than or equal to about 10:1, greater than orequal to about 11:1, or greater than or equal to about 12:1. In thecadmium free quantum dot, the mole ratio of a sum of selenium and sulfurwith respect to indium (i.e., (S+Se):In) may be less than or equal toabout 40:1, less than or equal to about 35:1, less than or equal toabout 30:1, less than or equal to about 25:1, less than or equal toabout 24:1, less than or equal to about 23:1, less than or equal toabout 22:1, less than or equal to about 21:1, less than or equal toabout 20:1, less than or equal to about 19:1, or less than or equal toabout 18:1.

The cadmium free quantum dot may have a size of greater than or equal toabout 6 nm, for example, greater than or equal to about 6.5 nm, greaterthan or equal to about 7.0 nm, greater than or equal to about 7.5 nm,greater than or equal to about 7.6 nm, greater than or equal to about7.7 nm, greater than or equal to about 7.8 nm, greater than or equal toabout 7.9 nm, or greater than or equal to about 8.0 nm. The cadmium freequantum dot may for example have a size of less than or equal to about20 nm, less than or equal to about 19 nm, less than or equal to about 18nm, less than or equal to about 17 nm, less than or equal to about 16nm, less than or equal to about 15 nm, less than or equal to about 14nm, less than or equal to about 13 nm, less than or equal to about 12nm, less than or equal to about 11 nm, less than or equal to about 10nm, or less than or equal to about 9 nm. The size of the quantum dot maybe a particle diameter. When the quantum dot does not have a sphericalshape, the size of the quantum dot may be a diameter, which iscalculated by converting a two-dimensional area confirmed by atransmission electron microscope analysis into a circle. As used herein,the term “size” may refer to a size of a single particle or an averagesize of the particles.

A quantum dot-based display device may exhibit improved color purity,luminance, and the like. For example, a liquid crystal display(hereinafter, LCD) realizes colors by polarized light passing anabsorption type color filter after passing a liquid crystal. LCD has aproblem of a narrow viewing angle and low light transmittance due to theabsorption type color filter. A quantum dot may emit light havingtheoretical quantum efficiency (QY) of about 100% and high color purity(e.g., less than or equal to about 40 nm of a full width at half maximum(FWHM)) and thus achieve increased luminous efficiency and improvedcolor reproducibility. The absorption type color filter may be replacedwith a photoluminescent type color filter including the quantum dot torealize a wider viewing angle and improved luminance.

The quantum dot may be dispersed in a host matrix (e.g., including apolymer and/or an inorganic material) to form a composite and thus beapplied it to a device. The quantum dot according to an embodiment hasimproved optical properties and process stability, and accordingly, whenincluded in a display device as a quantum dot polymer composite or itspatterned form, improved luminance, a wide viewing angle, and improvedcolor reproducibility may be realized. The quantum dot according to anembodiment has a relatively narrow full width at half maximum (FWHM) andaccordingly, may realize improved color reproducibility measured inaccordance with a BT2020 standard, which is a next generation standardof a display device. For example, a red light-emitting quantum dot witha full width at half maximum (FWHM) of greater than about 40 nm (e.g.,about 45 nm) may exhibit a color reproducibility of less than or equalto about 86% (R: 635 nm, G: 530 nm, Blue LED 448 nm, assuming the sameR/G full width at half maximum) measured in accordance with a BT2020standard. On the other hand, the red light-emitting quantum dot with afull width at half maximum (FWHM) of less than about 40 nm may exhibit acolor reproducibility of greater than or equal to about 88% (e.g.,greater than or equal to about 90%) measured in accordance with aBT2020.

A shape of the quantum dot is not particularly limited, may for examplebe a spherical, polyhedron, pyramid, multipod, or cube shape, nanotube,nanowire, nanofiber, nanosheet, or a combination thereof, but is notlimited thereto. The quantum dot may include the organic ligand and/orthe organic solvent which will be described below, on its surface. Theorganic ligand and/or the organic solvent may be bound to the surface ofthe quantum dot.

An embodiment provides a method of producing the above cadmium freequantum dot including

forming a first semiconductor nanocrystal shell on the semiconductornanocrystal core by reacting a zinc-containing precursor with aselenium-containing precursor at first reaction temperature for greaterthan or equal to about 40 minutes in the presence of the semiconductornanocrystal core including indium in a heated organic solvent andorganic ligand; and

forming a second semiconductor nanocrystal shell on the firstsemiconductor nanocrystal shell by reacting a zinc-containing precursor,a sulfur-containing precursor, and if necessary, a selenium precursor ata second reaction temperature in the presence of a particle having thefirst semiconductor nanocrystal shell formed on the semiconductornanocrystal core in the organic solvent and the organic ligand.

In this method, a total injection mole ratio of the zinc-containingprecursor relative to that of the indium may be greater than or equal toabout 15:1, for example, greater than or equal to about 16:1, greaterthan or equal to about 17:1, greater than or equal to about 18:1,greater than or equal to about 19:1, or greater than or equal to about20:1. In the method, a total injection mole ratio of the zinc-containingprecursor relative to that of the indium may be less than or equal toabout 50:1, less than or equal to about 45:1, less than or equal toabout 40:1, less than or equal to about 35:1, less than or equal toabout 30:1, or less than or equal to about 25:1.

Amounts of the selenium-containing precursor and the sulfur-containingprecursor with respect to the core may be adjusted so that the resultingcadmium free quantum dot may have the aforementioned composition and thestructure.

Details of the cadmium free quantum dot are the same as described above.

The organic ligand may include RCOOH, RNH₂, R₂NH, R₃N, RSH, RH₂PO,R₂HPO, R₃PO, RH₂P, R₂HP, R₃P, ROH, RCOOR′, RPO(OH)₂, RHPOOH, R₂HPOOH(wherein R and R′ are the same or different, and are independently ahydrogen, C1 to C40 aliphatic hydrocarbon group, such as C1 to C40(e.g., C3 to C24) alkyl or C2 to C40 (e.g., C3 to C24) alkenyl group, C2to C40 (e.g., C3 to C24) alkynyl group or a C6 to C40 aromatichydrocarbon group such as a C6 to C20 aryl group), a polymeric organicligand, or a combination thereof.

The organic ligand may coordinate to, e.g., be bound to, the surface ofthe obtained nanocrystal and help the nanocrystal to be well dispersedin the solution and/or may affect light emitting and electricalcharacteristics of quantum dots. Examples of the organic ligand mayinclude methane thiol, ethane thiol, propane thiol, butane thiol,pentane thiol, hexane thiol, octane thiol, dodecane thiol, hexadecanethiol, octadecane thiol, or benzyl thiol; methane amine, ethane amine,propane amine, butyl amine, pentyl amine, hexyl amine, octyl amine,dodecyl amine, hexadecyl amine, octadecyl amine, dimethyl amine, diethylamine, dipropyl amine; methanoic acid, ethanoic acid, propanoic acid,butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoicacid, dodecanoic acid, hexadecanoic acid, octadecanoic acid, oleic acid,or benzoic acid; phosphine such as substituted or unsubstituted methylphosphine (e.g., trimethyl phosphine, methyldiphenyl phosphine, etc.),substituted or unsubstituted ethyl phosphine (e.g., triethyl phosphine,ethyldiphenyl phosphine, etc.), substituted or unsubstituted propylphosphine, substituted or unsubstituted butyl phosphine, substituted orunsubstituted pentyl phosphine, or substituted or unsubstitutedoctylphosphine (e.g., trioctylphosphine (TOP)); phosphine oxide such assubstituted or unsubstituted methyl phosphine oxide (e.g., trimethylphosphine oxide, methyldiphenyl phosphineoxide, etc.), substituted orunsubstituted ethyl phosphine oxide (e.g., triethyl phosphine oxide,ethyldiphenyl phosphineoxide, etc.), substituted or unsubstituted propylphosphine oxide, substituted or unsubstituted butyl phosphine oxide, orsubstituted or unsubstituted octyl phosphine oxide (e.g.,trioctylphosphineoxide (TOPO); diphenyl phosphine, triphenyl phosphinecompound, or an oxide compound thereof; a mono- or di(C5 to C20alkyl)phosphinic acid such as mono- or dihexylphosphinic acid, mono- ordioctylphosphinic acid, mono- or didodecylphosphinic acid, mono- ordi(tetradecyl)phosphinic acid, mono- or di(hexadecyl)phosphinic acid,mono- or di(octadecyl)phosphinic acid, or a combination thereof; a C5 toC20 alkylphosphinic acid, a C5 to C20 alkylphosphonic acid such ashexylphosphonic acid, octylphosphonic acid, dodecylphosphonic acid,tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonicacid, or a combination thereof; and the like, but are not limitedthereto. One or more organic ligands may be used.

The solvent may a C6 to C22 primary amine such as hexadecylamine; a C6to C22 secondary amine such as dioctylamine; a C6 to C40 tertiary aminesuch as trioctylamine; a nitrogen-containing heterocyclic compound suchas pyridine; a C6 to C40 aliphatic hydrocarbon (e.g., alkane, alkene,alkyne, etc.) such as hexadecane, octadecane, octadecene, or squalane; aC6 to C30 aromatic hydrocarbon such as phenyldodecane,phenyltetradecane, or phenyl hexadecane; a phosphine substituted with aC6 to C22 alkyl group such as trioctylphosphine; a phosphine oxidesubstituted with a C6 to C22 alkyl group such as trioctylphosphineoxide; a C12 to C22 aromatic ether such as phenyl ether, or benzylether, or a combination thereof. Types and amounts of the solvent may beappropriately selected considering precursors and organic ligands.

A mixture of the organic solvent and the organic ligand may be heated ata predetermined temperature, for example, greater than or equal to about100° C., greater than or equal to about 120° C., greater than or equalto about 150° C., greater than or equal to about 200° C., greater thanor equal to about 250° C., or greater than or equal to about 270° C. andthe first reaction temperature or less for example, under a vacuumand/or inert atmosphere.

Details of the semiconductor nanocrystal core including the indium arethe same as set forth above. The semiconductor nanocrystal coreincluding the indium may further comprise phosphorous. The core may becommercially available or may be prepared in a suitable method. Thepreparation of the core is not particularly limited and may be performedin a suitable method of producing an indium phosphide based core. In anembodiment, the core may be synthesized in a hot injection mannerwherein a solution including a metal precursor (e.g., an indiumprecursor) and optionally a ligand is heated at a high temperature(e.g., of greater than or equal to about 200° C.) and then a phosphorousprecursor is injected the heated hot solution. In other embodiments, thesynthesis of the core may adopt a low temperature injection method. Theprepared core may be injected the heated organic solvent at atemperature of greater than or equal to about 100° C.

The zinc-containing precursor is not particularly limited and may bedesirably selected. For example, the zinc-containing precursor may be aZn metal powder, an alkylated Zn compound, Zn alkoxide, Zn carboxylate,Zn nitrate, Zn perchlorate, Zn sulfate, Zn acetylacetonate, Zn halide,Zn carbonate, Zn cyanide, Zn hydroxide, Zn oxide, Zn peroxide, or acombination thereof. Examples of the zinc-containing precursor may bedimethyl zinc, diethyl zinc, zinc acetate, zinc acetylacetonate, zinciodide, zinc bromide, zinc chloride, zinc fluoride, zinc carbonate, zincyanide, zinc nitrate, zinc oxide, zinc peroxide, zinc perchlorate, zincsulfate, and the like. One or more zinc-containing precursors may beused.

The selenium-containing precursor is not particularly limited and may bedesirably selected. For example, the selenium-containing precursorincludes selenium-trioctyl phosphine (Se-TOP), selenium-tributylphosphine (Se-TBP), selenium-triphenyl phosphine (Se-TPP),tellurium-tributylphosphine (Te-TBP), or a combination thereof but isnot limited thereto.

The first reaction temperature may be desirably selected. For example,the first reaction temperature may be greater than or equal to about280° C., greater than or equal to about 290° C., greater than or equalto about 300° C., greater than or equal to about 310° C., or greaterthan or equal to about 315° C. After or while the mixture including thesemiconductor nanocrystal core comprising indium and the zinc-containingprecursor is heated at the first reaction temperature, theselenium-containing precursor may be greater than or equal to once(e.g., twice or more, three times or more) added.

A reaction time at the first reaction temperature may be greater than orequal to about 40 minutes, for example, greater than or equal to about50 minutes, greater than or equal to about 60 minutes, greater than orequal to about 70 minutes, greater than or equal to about 80 minutes,greater than or equal to about 90 minutes and for example less than orequal to about 4 hours, less than or equal to about 3 hours, or lessthan or equal to about 2 hours.

The reaction at the first reaction temperature within the above timerange may form the first semiconductor nanocrystal shell to have athickness of greater than or equal to about three monolayers. Herein, anamount of the selenium precursor with respect to indium may be adjustedto form a first semiconductor nanocrystal shell having a predeterminedthickness for a predetermined reaction time. In the method of anembodiment, selenium may be used in an amount of greater than or equalto about 7 moles, greater than or equal to about 8 moles, or greaterthan or equal to about 9 mol based on about 1 mol of indium. The amountof selenium based on 1 mol of indium may be less than or equal to about20 mol or less than or equal to about 15 mol.

The method may not include cooling the reaction solution including aparticle having the first semiconductor nanocrystal shell down to atemperature below 100° C. (for example, of less than or equal to about50° C. (e.g., less than or equal to about 30° C. or room temperature).

The sulfur-containing precursor is not particularly limited and may bedesirably selected. The sulfur-containing precursor may be hexane thiol,octane thiol, decane thiol, dodecane thiol, hexadecane thiol, mercaptopropyl silane, sulfur-trioctylphosphine (S-TOP),sulfur-tributylphosphine (S-TBP), sulfur-triphenylphosphine (S-TPP),sulfur-trioctylamine (S-TOA), trimethylsilyl sulfur, sulfide ammonium,sodium sulfide, or a combination thereof. The sulfur-containingprecursor may be once or more (e.g., twice or more) injected.

For example, the second reaction temperature may be greater than orequal to about 280° C., greater than or equal to about 290° C., greaterthan or equal to about 300° C., greater than or equal to about 310° C.,or greater than or equal to about 315° C. After or while heated at thesecond reaction temperature, the sulfur-containing precursor may begreater than or equal to once (e.g., twice or more, or three times ormore) injected.

A reaction time at the second reaction temperature may be appropriatelyadjusted but is not particularly limited. For example, the reaction timeat the second reaction temperature may be greater than or equal to about30 minutes, greater than or equal to about 40 minutes, greater than orequal to about 50 minutes, greater than or equal to about 60 minutes,greater than or equal to about 70 minutes, greater than or equal toabout 80 minutes, or greater than or equal to about 90 minutes and lessthan or equal to about 4 hours, less than or equal to about 3 hours, orless than or equal to about 2 hours.

An amount of a sulfur precursor with respect to indium may be adjustedto form a second semiconductor nanocrystal shell having a predeterminedthickness for a predetermined reaction time. In an embodiment, an amountof sulfur per 1 mol of indium may be appropriately adjusted but notparticularly limited. For example, the amount of sulfur per 1 mol ofindium may be greater

than or equal to about 3 moles, greater than or equal to about 4 moles,greater than or equal to about 5 moles, greater than or equal to about 6moles, greater than or equal to about 7 moles, greater than or equal toabout 8 moles, greater than or equal to about 9 moles, greater than orequal to about 10 moles, greater than or equal to about 11 moles,greater than or equal to about 12 moles, greater than or equal to about13 moles, greater than or equal to about 14 moles, greater than or equalto about 15 moles, greater than or equal to about 16 moles, greater thanor equal to about 17 moles, greater than or equal to about 18 moles, orgreater than or equal to about 19 mol and less than or equal to about 40moles, less than or equal to about 35 moles, less than or equal to about30 moles, less than or equal to about 25 moles, less than or equal toabout 20 moles, or less than or equal to about 15 moles, but is notlimited thereto.

Amounts of the zinc containing precursor, the selenium-containingprecursor, and the sulfur-containing precursor based on indium of thecore may be selected considering the properties and the structure of theresulting cadmium free quantum dots.

When the non-solvent is added into the obtained final reaction solution,the organic ligand-coordinated nanocrystal may be separated (e.g.,precipitated). The non-solvent may be a polar solvent that is misciblewith the solvent used in the reaction and nanocrystals are notdispersible therein. The non-solvent may be selected depending on thesolvent used in the reaction and may be for example, acetone, ethanol,butanol, isopropanol, ethanediol, water, tetrahydrofuran (THF),dimethylsulfoxide (DMSO), diethylether, formaldehyde, acetaldehyde, asolvent having a similar solubility parameter to the foregoing solvents,or a combination thereof. The separation may be performed through acentrifugation, precipitation, chromatography, or distillation. Theseparated nanocrystal may be added to a washing solvent and washed, ifnecessary. The washing solvent has no particular limit and may have asimilar solubility parameter to that of the ligand and may, for example,include hexane, heptane, octane, chloroform, toluene, benzene, and thelike.

In an embodiment, a quantum dot composition includes the cadmium freequantum dot, optionally a binder polymer, a photopolymerizable monomerincluding a carbon-carbon double bond, and a photoinitiator. Thecomposition may further include an organic solvent.

In the composition, the cadmium free quantum dot is the same asdescribed above. In the composition, an amount of the quantum dot may bedesirably selected considering a final use and a composition of thecomposition. In an embodiment, the amount of the quantum dot may begreater than or equal to about 1 weight percent (wt %), for example,greater than or equal to about 2 wt %, greater than or equal to about 3wt %, greater than or equal to about 4 wt %, greater than or equal toabout 5 wt %, greater than or equal to about 6 wt %, greater than orequal to about 7 wt %, greater than or equal to about 8 wt %, greaterthan or equal to about 9 wt %, greater than or equal to about 10 wt %,greater than or equal to about 15 wt %, greater than or equal to about20 wt %, greater than or equal to about 25 wt %, greater than or equalto about 30 wt %, greater than or equal to about 35 wt %, or greaterthan or equal to about 40 wt % based on a solid content of thecomposition. The amount of the quantum dot may be less than or equal toabout 70 wt %, for example, less than or equal to about 65 wt %, lessthan or equal to about 60 wt %, less than or equal to about 55 wt %, orless than or equal to about 50 wt % based on a solid content of thecomposition.

In the composition according to an embodiment, the binder polymerincludes a carboxylic acid group. The binder polymer may include acopolymer of a monomer mixture including a first monomer including acarboxylic acid group and a carbon-carbon double bond, a second monomerincluding a carbon-carbon double bond and a hydrophobic moiety and notincluding a carboxylic acid group, and optionally a third monomerincluding a carbon-carbon double bond and a hydrophilic moiety and notincluding a carboxylic acid group;

a multiple aromatic ring-containing polymer having a backbone structurewhere two aromatic rings are bound to a quaternary carbon atom that is aconstituent atom of another cyclic moiety in the main chain andincluding a carboxylic acid group (—COOH); or

a combination thereof.

Examples of the first monomer may include unsaturated carboxylic acidsuch as acrylic acid, (meth)acrylic acid, maleic acid, itaconic acid,fumaric acid, 3-butenoic acid, and the like, but are not limitedthereto. The first monomer may be at least one compound.

Examples of the second monomer may be a carboxylic acid vinyl estercompound such as vinyl acetate or vinyl benzoate; an alkenyl aromaticcompound such as styrene, alpha-methyl styrene, vinyl toluene, or vinylbenzyl methyl ether; a unsaturated carbonic acid ester compound such asmethyl acrylate, methyl (meth)acrylate, ethyl acrylate, ethyl(meth)acrylate, butyl acrylate, butyl (meth)acrylate, benzyl acrylate,benzyl (meth)acrylate, cyclohexyl acrylate, cyclohexyl (meth)acrylate,phenyl acrylate, or phenyl (meth)acrylate; unsaturated carbonic acidamino alkyl ester compound such as 2-amino ethyl acrylate, 2-amino ethyl(meth)acrylate, 2-dimethyl amino ethyl acrylate, or 2-dimethyl aminoethyl (meth)acrylate; maleimides such as N-phenylmaleimide,N-benzylmaleimide, N-alkylmaleimide; a unsaturated carbonic acidglycidyl ester compound such as glycidyl acrylate or glycidyl(meth)acrylate; a vinyl cyanide compound such as acrylonitrile,methacrylonitrile; or a unsaturated amide compound such as acryl amideor methacryl amide, but are not limited thereto. As the second monomer,at least one compound may be used.

Specific examples of the third monomer may include 2-hydroxy ethylacrylate, 2-hydroxy ethyl (meth)acrylate, 2-hydroxy butyl acrylate, or2-hydroxy butyl (meth)acrylate, but are not limited thereto. As thethird monomer, at least one compound may be used.

In the carboxylic acid group-containing binder polymer, an amount of thefirst repeating unit derived from the first monomer may be greater thanor equal to about 10 mole percent (mol %), for example, greater than orequal to about 15 mol %, greater than or equal to about 25 mol %, orgreater than or equal to about 35 mol %. In the binder including acarboxyl group, an amount of the first repeating unit may be less thanor equal to about 90 mol %, for example, less than or equal to about 89mol %, less than or equal to about 80 mol %, less than or equal to about70 mol %, less than or equal to about 60 mol %, less than or equal toabout 50 mol %, less than or equal to about 40 mol %, less than or equalto about 35 mol %, or less than or equal to about 25 mol %.

In the carboxylic acid group-containing binder polymer, an amount of thesecond repeating unit derived from the second monomer may be greaterthan or equal to about 10 mol %, for example, greater than or equal toabout 15 mol %, greater than or equal to about 25 mol %, or greater thanor equal to about 35 mol %. In the binder polymer, an amount of thesecond a repeating unit may be less than or equal to about 90 mol %, forexample, less than or equal to about 89 mol %, less than or equal toabout 80 mol %, less than or equal to about 70 mol %, less than or equalto about 60 mol %, less than or equal to about 50 mol %, less than orequal to about 40 mol %, less than or equal to about 35 mol %, or lessthan or equal to about 25 mol %.

In the carboxylic acid group-containing binder polymer, an amount of thethird repeating unit derived from the third monomer may be greater thanor equal to about 1 mol %, for example, greater than or equal to about 5mol %, greater than or equal to about 10 mol % or greater than or equalto about 15 mol %, if it is present. In the binder polymer, an amount ofthe third repeating unit may be less than or equal to about 30 mol %,for example, less than or equal to about 25 mol %, less than or equal toabout 20 mol %, less than or equal to about 18 mol %, less than or equalto about 15 mol %, or less than or equal to about 10 mol %.

The carboxylic acid group-containing binder polymer may be a copolymerof (meth)acrylic acid; and at least one second/third monomer selectedfrom arylalkyl(meth)acrylate, hydroxyalkyl (meth)acrylate, and styrene.For example, the binder polymer may be a (meth)acrylic acid/methyl(meth)acrylate copolymer, a (meth)acrylic acid/benzyl (meth)acrylatecopolymer, a (meth)acrylic acid/benzyl (meth)acrylate/styrene copolymer,a (meth)acrylic acid/benzyl (meth)acrylate/2-hydroxy ethyl(meth)acrylate copolymer, or a (meth)acrylic acid/benzyl(meth)acrylate/styrene/2-hydroxy ethyl (meth)acrylate copolymer.

In an embodiment, the carboxylic acid group containing binder mayinclude a multi-aromatic ring-containing polymer. The multi-aromaticring-containing polymer may include a carboxylic acid group (—COOH) anda main chain having a backbone structure incorporated therein, whereinthe backbone structure includes a cyclic group including a quaternarycarbon atom, which is a part of the cyclic group, and two aromatic ringsbound to the quaternary carbon atom. The carboxylic acid group may bebonded to the main chain. The multi-aromatic ring-containing polymer isalso known as a cardo binder, which may be synthesized or commerciallyavailable (e.g., from Nippon Steel Chemical Co., Ltd.).

The binder polymer including the carboxylic acid may have an acid valueof greater than or equal to about 50 milligrams of potassium hydroxide(KOH) per gram (mg KOH/g). For example, the carboxylic acid-containingbinder polymer may have an acid value of greater than or equal to about60 mg KOH/g, greater than or equal to about 70 mg KOH/g, greater than orequal to about 80 mg KOH/g, greater than or equal to about 90 mg KOH/g,greater than or equal to about 100 mg KOH/g, greater than or equal toabout 110 mg KOH/g, greater than or equal to about 120 mg KOH/g, greaterthan or equal to about 125 mg KOH/g, or greater than or equal to about130 mg KOH/g. The acid value of the polymer may be for example less thanor equal to about 250 mg KOH/g, for example, less than or equal to about240 mg KOH/g, less than or equal to about 230 mg KOH/g, less than orequal to about 220 mg KOH/g, less than or equal to about 210 mg KOH/g,less than or equal to about 200 mg KOH/g, less than or equal to about190 mg KOH/g, less than or equal to about 180 mg KOH/g, or less than orequal to about 160 mg KOH/g, but is not limited thereto.

The binder polymer (e.g., containing the carboxylic acid group, such asthe carboxylic acid group-containing binder) may have a weight averagemolecular weight of greater than or equal to about 1000 g/mol, forexample, greater than or equal to about 2000 g/mol, greater than orequal to about 3000 g/mol, or greater than or equal to about 5000 g/mol.The binder polymer may have a weight average molecular weight of lessthan or equal to about 100000 g/mol, for example less than or equal toabout 50000 g/mol.

In the composition, an amount of the binder polymer may be greater thanor equal to about 0.5 wt %, for example, greater than or equal to about1 wt %, greater than or equal to about 5 wt %, greater than or equal toabout 10 wt %, greater than or equal to about 15 wt %, or greater thanor equal to about 20 wt % based on a total weight of the composition,but is not limited thereto. The amount of the binder polymer may be lessthan or equal to about 35 wt %, for example less than or equal to about33 wt %, or less than or equal to about 30 wt % based on a total weightof the composition. Within the ranges, dispersion of the quantum dot maybe ensured. The amount of the binder polymer may be about 0.5 wt % toabout 55 wt % based on a total weight of a solid content of thecomposition.

In the composition, the photopolymerizable monomer including acarbon-carbon double bond may include the photopolymerizable acryl-basedmonomer. The photopolymerizable acryl-based monomer may includealkyl(meth)acrylate, ethylene glycoldi(meth)acrylate, triethyleneglycoldi(meth)acrylate, diethylene glycoldi(meth)acrylate,1,4-butanedioldi(meth)acrylate, 1,6-hexanedioldi(meth)acrylate,neopentylglycoldi(meth)acrylate, pentaerythritoldi(meth)acrylate,pentaerythritoltri(meth)acrylate, pentaerythritoltetra(meth)acrylate,dipentaerythritoldi(meth)acrylate, dipentaerythritoltri(meth)acrylate,dipentaerythritolpenta(meth)acrylate, pentaerythritolhexa(meth)acrylate,bisphenol A di(meth)acrylate, bisphenol A epoxyacrylate,trimethylolpropanetri(meth)acrylate, ethylene glycolmonomethylether(meth)acrylate, novolacepoxy (meth)acrylate, dipropyleneglycoldi(meth)acrylate, triprophylene glycoldi(meth)acrylate, propyleneglycoldi(meth)acrylate, tris(meth)acryloyloxyethyl phosphate, or acombination thereof.

An amount of the photopolymerizable monomer may be greater than or equalto about 0.5 wt %, for example, greater than or equal to about 1 wt % orgreater than or equal to about 2 wt % based on a total weight of thecomposition. The amount of the photopolymerizable monomer may be lessthan or equal to about 30 wt %, for example, less than or equal to about28 wt %, less than or equal to about 25 wt %, less than or equal toabout 23 wt %, less than or equal to about 20 wt %, less than or equalto about 18 wt %, less than or equal to about 17 wt %, less than orequal to about 16 wt %, or less than or equal to about 15 wt % based ona total weight of the composition.

The (photo) initiator included in the composition of an embodiment maybe a compound that can initiate a radical polymerization of theacryl-based monomer ((meth)acrylate monomer) and/or a thiol compoundwhich will be described below (e.g., by light). Types of the initiatorare not particularly limited and may be selected appropriately. Forexample, the initiator may be a photo-initiator and may include atriazine compound, an acetophenone compound, a benzophenone compound, athioxanthone compound, a benzoin compound, an oxime compound, anaminoketone compound, a phosphine or phosphine oxide compound, acarbazole compound, a diketone compound, a sulfonium borate compound, adiazo compound, a diimidazole compound, or a combination thereof, but itis not limited thereto. As an alternative to, or in addition to theforegoing photoinitiators, a carbazole compound, a diketone compound, asulfonium borate compound, an azo compound (e.g., diazo compound), abiimidazole compound, or a combination thereof may be used as aphotoinitiator.

In the composition of an embodiment, an amount of the initiator may beadjusted in view of the type and the amount of the photopolymerizablemonomer as used. In an embodiment, the amount of the initiator may begreater than or equal to about 0.01 wt % or greater than or equal toabout 1 wt % and less than or equal to about 10 wt %, less than or equalto about 9 wt %, less than or equal to about 8 wt %, less than or equalto about 7 wt %, less than or equal to about 6 wt %, or less than orequal to about 5 wt % based on a total weight of the composition, but isnot limited thereto.

The composition may further include a (multiple or mono-functional)thiol compound having at least one thiol group at the terminal end, ametal oxide particulate, or a combination thereof.

When a plurality of metal oxide particles is present, the metal oxideparticulates may include TiO₂, SiO₂, BaTiO₃, Ba₂TiO₄, ZnO, or acombination thereof. An amount of the metal oxide fine particle may beless than or equal to about 25 wt %, less than or equal to about 20 wt%, less than or equal to about 15 wt % and greater than or equal toabout 1 wt %, or greater than or equal to about 5 wt % based on a totalsolid content of the composition. A particle size of the metal oxidefine particle is not particularly limited and may be selectedappropriately. The particle size of the metal oxide fine particles maygreater than or equal to about 100 nm, greater than or equal to about150 nm, or greater than or equal to about 200 nm and less than or equalto about 1,000 nm, less than or equal to about 900 nm, or less than orequal to about 800 nm.

The thiol compound may be a dithiol compound, a trithiol compound, atetrathiol compound, or a combination thereof. For example, the thiolcompound may be glycol di-3-mercaptopropionate (e.g., ethylene glycoldi-3-mercaptopropionate), glycol dimercapto acetate(e.g., ethyleneglycol dimercaptoacetate), trimethylolpropanetris(3-mercaptopropionate), pentaerythritol tetrakis (3-mercaptopropionate),pentaerythritol tetrakis (2-mercaptoacetate), 1,6-hexanedithiol,1,3-propanedithiol, 1,2-ethanedithiol, polyethylene glycol dithiolincluding 1 to 10 ethylene glycol repeating units, or a combinationthereof.

Based on a total weight of the composition, an amount of the thiolcompound may be less than or equal to about 50 wt %, less than or equalto about 40 wt %, less than or equal to about 30 wt %, less than orequal to about 20 wt %, less than or equal to about 10 wt %, less thanor equal to about 9 wt %, less than or equal to about 8 wt %, less thanor equal to about 7 wt %, less than or equal to about 6 wt %, or lessthan or equal to about 5 wt %. The amount of the thiol compound may begreater than or equal to about 0.1 wt %, for example, greater than orequal to about 0.5 wt %, greater than or equal to about 1 wt %, greaterthan or equal to about 2 wt %, greater than or equal to about 3 wt %,greater than or equal to about 4 wt %, greater than or equal to about 5wt %, greater than or equal to about 6 wt %, greater than or equal toabout 7 wt %, greater than or equal to about 8 wt %, greater than orequal to about 9 wt %, or greater than or equal to about 10 wt %, basedon a total weight of the composition.

The composition may further include an organic solvent and/or a liquidvehicle (hereinafter, simply referred to as “organic solvent”). Types ofthe usable organic solvent are not particularly limited. Types andamounts of the organic solvent may be appropriately determined byconsidering the above main components (i.e., the quantum dot, the COOHgroup-containing binder, the photopolymerizable monomer, thephotoinitiator, and if used, the thiol compound), and a type and anamount of an additive which is described below. The composition mayinclude a solvent in a residual amount except for a desired amount ofthe solid content (non-volatile components). The solvent may beappropriately selected by considering the other components (e.g., abinder, a photopolymerizable monomer, a photoinitiator, and otheradditives) in the composition, affinity for an alkali-developingsolution, a boiling point, and the like. Examples of the solvent mayinclude ethylene glycols such as ethylene glycol, diethylene glycol, orpolyethylene glycol; ethylene glycol ethers such as ethyleneglycolmonomethylether, ethylene glycolmonoethylether, diethyleneglycolmonomethylether, ethylene glycoldiethylether, or diethyleneglycoldimethylether; ethylene glycol ether acetates such as ethyleneglycolacetate, ethylene glycolmonoethyletheracetate, diethyleneglycolmonoethyletheracetate, or diethylene glycolmonobutyletheracetate;propylene glycol such as propylene glycol; propylene glycolethers suchas propylene glycolmonomethylether, propylene glycolmonoethylether,propylene glycol monopropylether, propyleneglycol monobutylether,propylene glycoldimethylether, dipropylene glycoldimethylether,propylene glycoldiethylether, or dipropylene glycoldiethylether;propylene glycoletheracetates such as propylene glycolmonomethyl etheracetate, or dipropylene glycolmonoethyletheracetate; amides such asN-methylpyrrolidone, dimethyl formamide, or dimethyl acetamide; ketonessuch as methylethylketone (MEK), methylisobutylketone (MIBK), orcyclohexanone; petroleums such as toluene, xylene, or solvent naphtha;esters such as ethyl acetate, butyl acetate, ethyl lactate, or ethyl3-ethoxy propionate; ethers such as diethyl ether, dipropyl ether, ordibutyl ether, chloroform, a C1 to C40 aliphatic hydrocarbon (e.g.,alkane, alkene, or alkyne), a halogen (e.g., chloro) substituted C1 toC40 aliphatic hydrocarbon (e.g., dichloroethane, trichloromethane, andthe like), a C6 to C40 aromatic hydrocarbon (e.g., toluene, xylene, andthe like), a halogen (e.g., chloro) substituted C6 to C40 aromatichydrocarbon, or a combination thereof.

If desired, the composition may further include various additives suchas a light diffusing agent, a leveling agent, or a coupling agent inaddition to the aforementioned components. The amount of the additive isnot particularly limited, and may be controlled within an appropriaterange wherein the additive does not cause an adverse effect onpreparation of the composition and production of the quantum dot-polymercomposite and optionally a patterning of the composite. The additivesmay be a compound or material having a desired function without aparticular limit.

If used, the additives may be used in an amount of greater than or equalto about 0.1 wt %, for example, greater than or equal to about 0.5 wt %,greater than or equal to about 1 wt %, greater than or equal to about 2wt %, or greater than or equal to about 5 wt % based on a total weightof the composition, but is not limited thereto. If used, the amount ofthe additives may be less than or equal to about 20 wt %, for example,less than or equal to about 19 wt %, less than or equal to about 18 wt%, less than or equal to about 17 wt %, less than or equal to about 16wt %, or less than or equal to about 15 wt % based on a total weight ofthe composition, but is not limited thereto.

The composition may be prepared by appropriately mixing the abovecomponents.

In an embodiment, a quantum dot-polymer composite includes a polymermatrix; and the above cadmium free quantum dot dispersed in the polymermatrix. The polymer matrix may be a cross-linked polymer, a binderpolymer having a carboxylic acid group, or a combination thereof. Thecross-linked polymer may include a thiolene resin, cross-linkedpoly(meth)acrylate, cross-linked polyurethane, a cross-linked epoxyresin, a cross-linked vinyl polymer, a cross-linked silicone resin, or acombination thereof. In an embodiment, the polymer matrix may include abinder polymer, a polymerization product of a photopolymerizable monomerincluding a carbon-carbon double bond, a polymerization product of thephotopolymerizable monomer and a multiple thiol compound having at leasttwo thiol groups (e.g., at a terminal end thereof), or a combinationthereof. The non-cadmium quantum dot, the binder polymer, thephotopolymerizable monomer, and the multiple thiol compound are the sameas described above.

The quantum dot polymer composite may have a form of a film. The filmmay have, for example, a thickness of less than or equal to about 30 μm,for example, less than or equal to about 10 μm, less than or equal toabout 8 μm, or less than or equal to about 7 μm and greater than about 2μm, for example, greater than or equal to about 3 μm, greater than orequal to about 3.5 μm, or greater than or equal to about 4 μm. Thequantum dot polymer composite may exhibit improved thermal stability.Accordingly, the quantum dot polymer composite may exhibitphoto-conversion efficiency (PCE) of greater than or equal to about 20%when heat-treated at about 180° C. for about 30 minutes under a nitrogenatmosphere.

In an embodiment, a display device includes a light source and a lightemitting element (e.g., a photoluminescent element), and the lightemitting element includes the above quantum dot-polymer composite, andthe light source is configured to provide the light emitting elementwith incident light. The incident light may have a photoluminescencepeak wavelength of greater than or equal to about 440 nm, for example,greater than or equal to about 450 nm and less than or equal to about460 nm.

In an embodiment, the light emitting element may include a sheet of thequantum dot polymer composite. The display device may further include aliquid crystal panel and the sheet of the quantum dot polymer compositemay be disposed between the light source and the liquid crystal panel.FIG. 3 shows an exploded view of a display device. Referring to FIG. 3,the display device may have a structure wherein a reflector, a lightguide panel (LGP) and a blue LED light source (Blue-LED), the quantumdot-polymer composite sheet (QD sheet), and various optical films suchas a prism, double brightness enhance film (DBEF), and the like arestacked, and a liquid crystal panel is disposed thereon.

In an embodiment, the display device may include a stacked structureincluding a (e.g., transparent) substrate and a light emitting layer(e.g., a photoluminescent layer) disposed on the substrate as a lightemitting element. In the stacked structure, the light emitting layerincludes a pattern of the quantum dot polymer composite, and the patternmay include at least one repeating section configured to emit light of apredetermined wavelength. The pattern of the quantum dot polymercomposite may include a first repeating section that may emit a firstlight, a second repeating section that may emit a second light, or acombination thereof.

The first light and the second light have a different maximumphotoluminescence peak wavelength in a photoluminescence spectrum. In anembodiment, the first light may be red light (R) having a maximumphotoluminescence peak wavelength of about 600 nm to about 650 nm (e.g.,about 620 nm to about 650 nm), the second light may be green light (G)having a maximum photoluminescence peak wavelength of about 500 nm toabout 550 nm (e.g., about 510 nm to about 550 nm), or vice versa (i.e.,the first light may be a green light and the second light may be a redlight).

The substrate may be a substrate including an insulation material. Thesubstrate may include a material of glass; various polymers such as apolyester (e.g., poly(ethylene terephthalate) (PET), poly(ethylenenaphthalate) (PEN), or the like), polycarbonate, a poly(C1 toC10(meth)acrylate), polyimide, polyamide, or a combination thereof (acopolymer or a mixture thereof); polysiloxane (e.g., PDMS); an inorganicmaterial such as Al₂O₃ or ZnO; or a combination thereof, but is notlimited thereto. A thickness of the substrate may be desirably selectedconsidering a substrate material but is not particularly limited. Thesubstrate may have flexibility. The substrate may have a transmittanceof greater than or equal to about 50%, greater than or equal to about60%, greater than or equal to about 70%, greater than or equal to about80%, or greater than or equal to about 90% for light emitted from thequantum dot.

At least a portion of the substrate may be configured to cut (absorb orreflect) blue light. A layer capable of blocking (e.g., absorbing orreflecting) blue light, also referred to herein as a “blue cut layer” or“blue light absorption layer”, may be disposed on at least one surfaceof the substrate. For example, the blue cut layer (blue light absorptionlayer) may include an organic material and a predetermined dye, such as,for example, a yellow dye or a dye capable of absorbing blue light andtransmitting green and/or red light.

In an embodiment, a method of producing the stacked structure includes

forming a film of the above composition on a substrate;

exposing a selected region of the film to light (e.g., having awavelength of less than or equal to about 400 nm); and

developing the exposed film with an alkali developing solution to obtaina pattern of the quantum dot polymer composite.

The details of the substrate and the composition are the same asdescribed above.

A method of forming a pattern of the quantum dot polymer composite isexplained with reference to FIG. 4.

The composition is coated to have a predetermined thickness on asubstrate in an appropriate method of spin coating, slit coating, andthe like (S1). If desired, the formed film may be pre-baked (PRB, S2).Conditions (such as a temperature, a duration, and an atmosphere) forthe pre-baking may be selected appropriately.

The formed (and optionally, pre-baked) film is exposed to light of apredetermined wavelength (UV light) under a mask having a predeterminedpattern (EXP, S3). The wavelength and the intensity of light may beselected depending on the types and the amounts of the photoinitiator,the types and the amounts of quantum dots, or the like.

The film having the exposed selected area is treated (e.g., sprayed orimmersed) with an alkali developing solution, and thereby the unexposedregion in the film is dissolved to provide a desired pattern, thisprocess being referred to as development (DEV) (S4). The obtainedpattern may be post-baked (S5, FOB), if desired, for example, at atemperature of about 150° C. to about 230° C. for a predetermined time,for example, greater than or equal to about 10 min or greater than orequal to about 20 min, in order to improve crack resistance and solventresistance of the pattern,

When the quantum dot-polymer composite pattern has a plurality ofrepeating sections, a quantum dot-polymer composite having a desiredpattern may be obtained by preparing a plurality of compositionsincluding a quantum dot (e.g., a red light emitting quantum dot, a greenlight emitting quantum dot, or optionally, a blue light emitting quantumdot) having desired photoluminescence properties (a photoluminescencepeak wavelength and the like) to form each repeating section andrepeating the pattern formation process for each of the composition asmany times (e.g., twice or more or three times or more) as required toform a desired pattern of the quantum dot polymer composite (S6).

In an embodiment, an ink composition of an embodiment including thepopulation of the cadmium free quantum dots and the liquid vehicle maybe used to form a pattern. For example, a pattern may be formed bydepositing the ink composition including a plurality of cadmium freequantum dots, a liquid vehicle, and a monomer on a desired region of asubstrate, optionally removing the liquid vehicle and conducting apolymerization.

For example, the quantum dot-polymer composite may be in the form of apattern of at least two different repeating color sections (e.g., RGBsections). Such a quantum dot-polymer composite pattern may be used as aphotoluminescence-type color filter in a display device.

In other embodiments, a display device includes a light source and alight emitting element including a stacked structure (hereinafter, alsoreferred to as a layered structure).

The light source may be configured to provide incident light to thelight emitting element including the layered structure. The incidentlight may have a wavelength of about 440 nm to about 480 nm such asabout 440 nm to about 470 nm. The incident light may be a third light.

In a display device including the stacked structure, the light sourcemay include a plurality of light emitting units respectivelycorresponding to the first section and the second section, and the lightemitting units may include a first electrode and a second electrodefacing each other and an electroluminescent layer disposed between thefirst electrode and the second electrode. The electroluminescent layermay include an organic light emitting material.

For example, each light emitting unit of the light source may include anelectroluminescent device (e.g., an organic light emitting diode (OLED))structured to emit light of a predetermined wavelength (e.g., bluelight, green light, or a combination thereof). Structures and materialsof the electroluminescent device such as the organic light emittingdiode (OLED) are not particularly limited.

FIG. 5A and FIG. 5B show a schematic cross-sectional view of a displayincluding a layered structure of an embodiment. Referring to FIG. 5A andFIG. 5B, the light source may include an organic light emitting diodeOLED. For example, the OLED may emit blue light or a light having awavelength in a region of about 500 nm or less. The organic lightemitting diode OLED may include (at least two, for example, three) pixelelectrodes 90 a, 90 b, 90 c formed on a substrate 100, a pixel defininglayer 150 a, 150 b formed between the adjacent pixel electrodes 90 a, 90b, 90 c, an organic light emitting layer 140 a, 140 b, 140 c formed onthe pixel electrodes 90 a, 90 b, 90 c, and a common electrode layer 130formed on the organic light emitting layer 140 a, 140 b, 140 c.

A thin film transistor and a substrate may be disposed under the organiclight emitting diode. The pixel areas of the OLED may be disposedcorresponding to the first, second, and third sections that will bedescribed in detail below, respectively.

The stacked structure that includes a quantum dot-polymer compositepattern (e.g., including a first repeating section including green lightemitting quantum dots and/or a second repeating section including redlight emitting quantum dots) and a substrate, or the quantum dot-polymercomposite pattern, may be disposed on or over a light source, forexample, directly on the light source.

The light (e.g., blue light) emitted from the light source may enter thesecond section 21 and the first section 11 of the pattern 170 to emit(e.g., converted) red light R and green light G, respectively. The bluelight B emitted from the light source passes through or transmits fromthe third section 31. Over the second section 21 emitting red lightand/or the first section 11 emitting green light, an optical element 160may be disposed. The optical element may be a blue cut layer which cuts(e.g., reflects or absorbs) blue light and optionally green light, or afirst optical filter. The blue cut layer 160 may be disposed on theupper substrate 240. The blue cut layer 160 may be disposed between theupper substrate 240 and the quantum dot-polymer composite pattern andover the first section 11 and the second section 21. Details of the bluecut layer are the same as set forth for the first optical filter 310below.

The aforementioned device of an embodiment may be fabricated byseparately preparing the layered structure and the OLED (for example,the blue OLED), respectively, and combining them. Alternatively, thedevice may be fabricated by directly forming the pattern of the quantumdot-polymer composite over the OLED.

In an embodiment, the display device may further include a lowersubstrate 210, an optical element (e.g., polarizer) 300 disposed belowthe lower substrate 210, and a liquid crystal layer 220 interposedbetween the layered structure and the lower substrate 210. The layeredstructure may be disposed in such a manner that a light emitting layer(i.e., the quantum dot-polymer composite pattern) faces the liquidcrystal layer. The display device may further include an optical element(e.g., polarizer) 300 between the liquid crystal layer 220 and the lightemitting layer. The light source may further include an LED andoptionally a light guide panel.

Referring to FIG. 6, in an embodiment, the display device includes aliquid crystal panel 200, a lower optical element 300 (e.g., polarizer)disposed on and/or under the liquid crystal panel 200, and a backlightunit including a blue light emitting light source 110 under a loweroptical element 300. The backlight unit may include a light source 110and a light guide panel 120 (edge type). Alternatively, the backlightunit may be a direct light source without a light guide panel. Theliquid crystal panel 200 may include a lower substrate 210, an uppersubstrate 240, and a liquid crystal layer 220 between the upper andlower substrates, and a light emitting layer (color filter layer) 230disposed on or under the upper substrate 240. The light emitting layer230 may include the quantum dot-polymer composite (or a patternthereof).

A wire plate 211 is provided on an internal surface, for example, on theupper surface of the lower substrate 210. The wire plate 211 may includea plurality of gate wires and data wires that define a pixel area, athin film transistor disposed adjacent to a crossing region of gatewires and data wires, and a pixel electrode for each pixel area, but isnot limited thereto. Details of such a wire plate are not particularlylimited.

The liquid crystal layer 220 may be disposed on the wire plate 211. Theliquid crystal layer 220 may include an alignment layer 221 on an uppersurface of the liquid crystal layer 220 and on a lower surface of theliquid crystal layer 220, to initially align the liquid crystal materialincluded therein. Details regarding a liquid crystal material, analignment layer material, a method of forming an alignment layer, amethod of forming a liquid crystal layer, a thickness of liquid crystallayer, or the like are not particularly limited.

In an embodiment, an upper optical element or an upper polarizer 300 maybe provided between the liquid crystal layer 220 and the upper substrate240, but it is not limited thereto. For example, the upper opticalelement or upper polarizer 300 may be disposed between the liquidcrystal layer 220 (or a common electrode 231) and the light emittinglayer (or the quantum dot-polymer composite pattern). A black matrix 241may be provided under the upper substrate 240 (e.g., on a lower surfacethereof). Openings within the black matrix 241 are aligned with (orprovided to hide) a gate line, a data line, and a thin film transistorof a wire plate 211 on the lower substrate 210. A second section (R)including a color filter emitting red light, a first section (G)including a color filter emitting green light and/or a third section (B)including a color filter for emitting or transmitting blue light may bedisposed in the openings within the black matrix 241 (BM). For example,the black matrix 241 may have a lattice shape. If desired, the lightemitting layer may further include at least one of a fourth repeatingsection. The fourth repeating section may be configured to emit lighthaving a color (e.g., cyan, magenta, yellow, or the like) different fromthe colors of the light emitted from the first to third sections.

The light emitting layer (color filter layer) 230 may be on atransparent common electrode 231.

If desired, the display device may further include a blue cut filter310, hereinafter, also referred to as a first optical filter layer 310.The first optical filter layer 310 may be disposed between uppersurfaces of the second section (R) and the first section (G) and thelower surface of the upper substrate 240, or on an upper surface of theupper substrate (240). The first optical filter layer 310 may include asheet having openings that correspond to the third section (B) (e.g., apixel area showing, e.g., emitting, a blue color) and may be formed onportions corresponding to the first and second sections (G, R). Thefirst optical filter layer 310 may be formed as a single body structureover the portions of the light emitting layer 230 corresponding to thefirst and second sections (G, R), and which are other than the portionsoverlapping the third section, but is not limited thereto.Alternatively, at least two first optical filter layers may be spacedapart from each other and may be disposed over each of the portionsoverlapping the first and the second sections, respectively.

For example, the first optical filter layer may block light having apredetermined wavelength range in the visible light range and maytransmit light having another wavelength range. For example, the firstoptical filter layer may block blue light and transmit light other thanblue light. For example, the first optical filter layer may transmitgreen light, red light, or yellow light (e.g., the mixed light of thegreen light and the red light).

The first optical filter layer may include a polymer thin film includinga dye and/or a pigment that absorbs light having a specific wavelength,i.e., the wavelength to be blocked. The first optical filter layer mayblock at least 80%, or at least 90%, even at least 95% of blue lighthaving a wavelength of less than or equal to about 480 nm. With respectto the visible light having other wavelengths, the first optical filterlayer may have a light transmittance of greater than or equal to about70%, for example, greater than or equal to about 80%, greater than orequal to about 90%, or even up to 100%.

The first optical filter layer may absorb and substantially block bluelight having a wavelength of less than or equal to about 500 nm, and forexample, may selectively transmit green light or red light. In thiscase, at least two first optical filter layers may be spaced apart anddisposed on each of the portions overlapping the first and secondsections, respectively. For example, the first optical filter layerselectively transmitting red light may be disposed on the portionoverlapping the section emitting red light and the first optical filterlayer selectively transmitting green light may be disposed on theportion overlapping the section emitting green light.

In an embodiment, the first optical filter layer may include at leastone of a first region and a second region. The first region of the firstoptical filter layer blocks (e.g., absorbs) blue light and red light andtransmits light having a wavelength of a predetermined range, e.g., awavelength greater than or equal to about 500 nm, greater than or equalto about 510 nm, or greater than or equal to about 515 nm, and less thanor equal to about 550 nm, less than or equal to about 540 nm, less thanor equal to about 535 nm, less than or equal to about 530 nm, less thanor equal to about 525 nm, or less than or equal to about 520 nm. Thesecond region of the first optical filter layer blocks (e.g., absorb)blue light and green light and transmits light having a wavelength of apredetermined range, e.g., a wavelength of greater than or equal toabout 600 nm, greater than or equal to about 610 nm, or greater than orequal to about 615 nm and less than or equal to about 650 nm, less thanor equal to about 640 nm, less than or equal to about 635 nm, less thanor equal to about 630 nm, less than or equal to about 625 nm, or lessthan or equal to about 620 nm. The first region of the first opticalfilter layer may be disposed (directly) on or over a locationoverlapping a green light emitting section and the second region of thefirst optical filter layer may be disposed (directly) on or over alocation overlapping a red light emitting section. The first region andthe second region may be optically isolated from one another, forexample, by a black matrix. The first optical filter layer maycontribute to improving the color purity of a display device.

The first optical filter layer may be a reflection type filter includinga plurality of layers (e.g., inorganic material layers) each having adifferent refractive index. For example, in the first optical layer, twolayers having different refractive indices may be alternately stacked oneach other. For example, a layer having a high refractive index and alayer having a low refractive index may be alternately laminated witheach other.

The display device may further include a second optical filter layer 311(e.g., red/green light or yellow light recycling layer) that is disposedbetween the light emitting layer 230 and the liquid crystal layer 220,and between the light emitting layer 230—(e.g., the quantum dot polymercomposite layer) and the upper polarizer 300. The second optical filterlayer 311 may transmit at least a portion of a third light, and reflectat least a portion of a first light and/or a second light. The secondoptical filter layer may reflect light having a wavelength of greaterthan 500 nm. The first light may be green (or red) light, the secondlight may be red (or green) light, and the third light may be bluelight.

The display device may exhibit improved luminance (e.g., greater than orequal to about 100 nits (candelas per square meter)) and a wide viewingangle (e.g., greater than or equal to about 160°).

An embodiment provides an electronic device including the quantum dot.The electronic device may include a light emitting diode (LED), anorganic light emitting diode (OLED), a sensor, a solar cell, an imagingsensor, or a liquid crystal display (LCD), but is not limited thereto.

Hereinafter, the embodiments are illustrated in more detail withreference to examples. However, they are exemplary examples of thepresent disclosure, and the present disclosure is not limited thereto.

EXAMPLES Analysis Method 1. Ultraviolet-Visible (UV-Vis) SpectroscopyAnalysis

An Agilent Cary 5000 spectrometer is used to perform an ultraviolet (UV)spectroscopy analysis and obtain an UV-Visible absorption spectrum.

2. Photoluminescence Analysis

A Hitachi F-7000 spectrometer is used to obtain a photoluminescence (PL)spectrum of the produced quantum dots with an excitation light having awavelength of 450 nanometers (nm).

3. Absolute Quantum Efficiency (Quantum Yield) of Quantum Dot

Quantum efficiency is obtained by dividing the number of photons emittedalong with photoluminescence from a sample by the number of photonsabsorbed by the sample. The quantum efficiency is measured with respectto the quantum dot dispersion or a quantum dot-polymer composite byusing HAMAMATSU-Quantaurus-QY, C11347 (Hamamatsu Corp.).

4. ICP-AES Analysis

Inductively coupled plasma atomic emission spectroscopy (ICP-AES)analysis is performed by using Shimadzu ICPS-8100.

5. Quantum Efficiency of Composite Film

Quantum efficiency of a composite film is measured by putting thecomposite film in an integrating sphere and irradiating the same withexcitation light of a wavelength of 450 nm.

6. TEM Analysis

A Titan ChemiSTEM electron microscope is used to perform a transmissionelectron microscope analysis to measure the particle size of the quantumdot.

Reference Example 1

Indium acetate and palmitic acid are dissolved in 1-octadecene in a 200millimeter (mL) reaction flask, and the solution is heated at 120° C.under vacuum. Indium and palmitic acid are used in a mole ratio of 1:3.After one hour, an atmosphere in the reactor is converted into nitrogen.After heating the reactor at 280° C., a mixed solution oftris(trimethylsilyl)phosphine (TMS3P) and trioctylphosphine is rapidlyinjected thereinto, and the mixture is reacted for 20 minutes. Thereaction solution is rapidly cooled down to room temperature, acetone isadded thereto, the mixture is centrifuged to obtain a precipitate, andthe precipitate is dispersed in toluene again. An amount of TMS3P is 0.5moles (mol) per 1 mol of indium. An amount of TOP is 0.1 moles to 10moles (e.g. 0.5 mole) per 1 mole of indium. An InP core obtainedtherefrom has a size of about 3 nm.

Example 1

(1) Selenium is dispersed in trioctylphosphine to prepare a Se/TOP stocksolution, and sulfur is dispersed in trioctylphosphine to prepare aS/TOP stock solution.

Zinc acetate and oleic acid are dissolved in trioctylamine in a 200 mLreaction flask, and the solution is vacuum-treated at 120° C. for 10minutes. After substituting the atmosphere inside the reaction flaskwith N₂, a dispersion of InP semiconductor nanocrystals in toluene isadded to the solution, while the solution is heated up to 320° C., theSe/TOP and optionally, the zinc acetate are three times injected intothe reaction flask. The reaction proceeds to obtain a reaction solutionincluding a particle having a ZnSe shell disposed on the core. A totalreaction time is 80 minutes.

Subsequently, an S/TOP stock solution and the zinc acetate are injectedinto the reaction solution at the reaction temperature of 320° C. Areaction is performed to obtain a reaction solution including a particlehaving a ZnS shell disposed on the ZnSe shell. A total reaction time is80 minutes.

In the reaction, a total amount of Se is 7.5 moles, a total amount of Sis 13.9 moles, and a total amount of zinc is 16 mol based on 1 mol ofindium.

An excess amount of ethanol is added to a reactant including theobtained core/multi-layered shell quantum dot, and the mixture iscentrifuged. After the centrifugation, a supernatant is discardedtherefrom, a precipitate therein is dried and then dispersed inchloroform or toluene to obtain a quantum dot solution (hereinafter, aQD solution).

(2) An ICP-AES analysis of the obtained QD is performed, and the resultis shown in Table 1. A TEM analysis, a UV-vis spectroscopy analysis, anda photoluminescence analysis of the QD are performed. The results areshown in Table 2.

Example 2

A core/multi-layered shell quantum dot is obtained according to the samemethod as Example 1 except for using 9.7 mol of Se, 20.7 mol of S, and21 mol of zinc based on 1 mol of indium.

An ICP-AES analysis of the QD performed, and the result is shown inTable 1. A TEM analysis, a UV-vis spectroscopy analysis, and aphotoluminescence analysis of the QD are performed. The results areshown in Table 2.

Example 3

A core/multi-layered shell quantum dot is obtained according to the samemethod as Example 1 except for using 8.2 mol of Se, 11.5 mol of S, and17 mol of zinc based on 1 mol of indium.

An ICP-AES analysis of the obtained QD is performed, and the result isshown in Table 1. A TEM analysis, a UV-vis spectroscopy analysis, and aphotoluminescence analysis of the QD are performed. The results areshown in Table 2.

Example 4

A core/multi-layered shell quantum dot is obtained according to the samemethod as Example 1 except for using 10 mol of Se, 17.6 mol of S, and 21mol of zinc based on 1 mol of indium.

An ICP-AES analysis of the obtained QD is performed, and the result isshown in Table 1. A TEM analysis, a UV-vis spectroscopy analysis, and aphotoluminescence analysis of the QD are performed. The results areshown in Table 2.

Comparative Example 1

A core/multi-layered shell quantum dot is obtained according to the samemethod as Example 1 except for using 5.6 mol of Se, 15 mol of S, and14.5 mol of zinc based on 1 mol of indium.

An ICP-AES analysis of the obtained QD is performed, and the result isshown in Table 1. A TEM analysis, a UV-vis spectroscopy analysis, and aphotoluminescence analysis of the QD are performed. The results areshown in Table 2.

Comparative Example 2

A core/multi-layered shell quantum dot is obtained according to the samemethod as Example 1 except for using 6.2 mol of Se, 15.4 mol of S, and16.7 mol of zinc based on 1 mol of indium.

An ICP-AES analysis of the obtained QD is performed, and the result isshown in Table 1. A TEM analysis, a UV-vis spectroscopy analysis, and aphotoluminescence analysis of the QD are performed. The results areshown in Table 2.

Comparative Example 3

A core/multi-layered shell quantum dot is obtained according to the samemethod as Example 1 except for using 1.7 mol of Se, 6.2 mol of S, and 9mol of zinc based on 1 mol of indium.

ICP-AES analyses of the obtained QDs are performed, and the results areshown in Table 1. A TEM analysis, a UV-vis spectroscopy analysis, and aphotoluminescence analysis of the QD are performed. The results areshown in Table 2.

TABLE 1 Relative Mole Amount P/In (S + Se)/In Zn/In Se/In In Comparative0.82 9.66 11.23 5.09 1.00 Example 1 Comparative 0.76 10.3 12.45 5.641.00 Example 2 Comparative — 3.5 5.3 1.6 1.00 Example 3 Example 1 0.7611 12.56 6.79 1.00 Example 2 0.63 15.15 16.63 8.80 1.00 Example 3 0.7610.96 12.58 7.47 1.00 Example 4 0.81 14.36 16.42 9.02 1.00

TABLE 2 PL HWHM FWHM QY Size Wavelength VD (nm) (nm) (%) (nm) (nm)Comparative 0.04 27 41 87 7.2 629 Example 1 Comparative 0.182 25 41 827.6 628 Example 2 Comparative 0.33 28 44 56 5.6 621 Example 3 Example 10.261 24 39 89 7.7 630 Example 2 0.33 24 38 90 8.5 631 Example 3 0.35522 38 90 8.1 631 Example 4 0.449 21 36 90 8.7 628

Referring to the results of the tables, the quantum dots according toexample embodiments have a relatively large VD and exhibit improvedluminous efficiency and a low full width at half maximum (FWHM) comparedwith the quantum dots according to Comparative Examples.

Experimental Example: Quantum Dot Polymer Composite and its Pattern

Each quantum dot chloroform dispersion according to Example 4 andComparative Example 3 is mixed with a binder (a quaternary copolymer ofmethacrylic acid, benzyl methacrylate, 2-hydroxyethylmethacrylate, andstyrene, an acid value: 130 mg KOH/g, a molecular weight: 8000 g/mol, amethacrylic acid:benzylmethacrylate:2-hydroxyethylmethacrylate:styrene(a mole ratio)=61.5:12:16.3:10.2) solution (solvent: propylene glycolmonomethyl ether acetate (PGMEA) having a concentration of 30 weightpercent (wt %)) to prepare quantum dot-binder dispersion.

The quantum dot binder dispersion is mixed with hexaacrylate having thefollowing structure as a photopolymerizable monomer, ethylene glycoldi-3-mercaptopropionate (hereinafter, 2T), an oximeester compound as aninitiator, TiO₂ as a light diffusing agent and PGMEA to prepare acomposition.

The composition includes 40 wt % of the quantum dot, 12.5 wt % of thebinder polymer, 25 wt % of 2T, 12 wt % of the photopolymerizablemonomer, 0.5 wt % of the initiator, and 10 wt % of the light diffusingagent based on a solid content of the composition, and a total solidcontent is 25%.

Each photosensitive composition is spin-coated on a glass substrate at150 revolutions per minute (rpm) for 5 seconds to obtain films. Thefilms are pre-baked (PRB) at 100° C. These pre-baked films are exposedto irradiation of light (a wavelength: 365 nm, intensity: 100millijoules (mJ)) for 1 second under a mask having a predeterminedpattern (e.g., a square dot or a stripe pattern), developed in apotassium hydroxide aqueous solution (a concentration: 0.043%) for 50seconds to obtain quantum dot-polymer composite patterns (a thickness: 6micrometers (μm)).

The obtained pattern is heat-treated (i.e., post-baked, FOB) at 180° C.for 30 minutes under a nitrogen atmosphere.

Quantum efficiency after PRB and FOB and a process maintenance of theobtained film (composite) are measured and calculated, and the resultsare shown in Table 3.

TABLE 3 Quantum Quantum efficiency efficiency Process after PRB afterPOB maintenance (%) (%) (%) Example 4 30 23.8 79 Comparative Example 329.1 19.1 66

The process maintenance is a percentage of the quantum efficiency afterFOB relative to the quantum efficiency after PRB.

Referring to the results of Table 3, the quantum dot-polymer compositepattern including the quantum dot according to Example 4 exhibitsimproved photo-conversion efficiency and stability (i.e., a processmaintenance rate) compared with the quantum dot-polymer compositepattern including the quantum dot according to Comparative Example 3.

While this disclosure has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A cadmium free quantum dot, wherein the cadmiumfree quantum dot comprises indium and zinc, wherein the cadmium freequantum dot does not comprise cadmium, wherein the cadmium free quantumdot has a maximum photoluminescence peak in a red light wavelengthregion, wherein an ultraviolet-visible absorption spectrum of thecadmium free quantum dot has a valley between about 450 nanometers and afirst absorption peak wavelength, and in the ultraviolet-visibleabsorption spectrum of the cadmium free quantum dot, a valley depthdefined by the following equation is greater than or equal to about 0.2:(Abs_(first)−Abs_(valley))/Abs_(first)=valley depth wherein, Abs_(first)is an absorption intensity at the first absorption peak wavelength andAbs_(valley) is an absorption intensity at a lowest point of the valley.2. The cadmium free quantum dot of claim 1, wherein the cadmium freequantum dot comprises a first semiconductor nanocrystal comprisingindium and phosphorus and a second semiconductor nanocrystal comprisinga zinc selenide, a zinc sulfide, a zinc selenide sulfide, or acombination thereof.
 3. The cadmium free quantum dot of claim 2, whereinthe second semiconductor nanocrystal is disposed on the firstsemiconductor nanocrystal.
 4. The cadmium free quantum dot of claim 1,wherein the cadmium free quantum dot has a size of greater than or equalto about 6 nanometers.
 5. The cadmium free quantum dot of claim 1,wherein the red light wavelength region is greater than or equal toabout 600 nanometers and less than or equal to about 650 nanometers. 6.The cadmium free quantum dot of claim 1, wherein a full width at halfmaximum of the maximum photoluminescence peak is less than or equal toabout 40 nanometers.
 7. The cadmium free quantum dot of claim 1, whereina half width at half maximum of the first absorption peak is less thanor equal to about 25 nanometers.
 8. The cadmium free quantum dot ofclaim 1, wherein the valley depth is in a range of greater than or equalto about 0.26 to 0.449.
 9. The cadmium free quantum dot of claim 1,wherein a quantum efficiency of the cadmium free quantum dot is greaterthan or equal to about 80%.
 10. The cadmium free quantum dot of claim 1,wherein in the cadmium free quantum dot, a mole ratio of the zinc to theindium is greater than or equal to about 10:1 and less than or equal toabout 40:1, a mole ratio of selenium with respect to indium is greaterthan or equal to about 5.7:1, a mole ratio of zinc with respect toindium is greater than or equal to about 12.5:1, or a ratio of a totalmole amount of sulfur and selenium to a mole amount of indium is greaterthan or equal to about 3:1 and less than or equal to about 40:1.
 11. Anink comprising: a plurality of quantum dots, and a liquid vehicle,wherein the plurality of quantum dots comprises the cadmium free quantumdots of claim
 1. 12. A display device comprising a light emittingelement and a light source, wherein the light source is configured toprovide light with the light emitting element, wherein the lightemitting element comprises a plurality of the cadmium free quantum dotsof claim 1 wherein the light emitting element comprises a light emittinglayer disposed over the light source.
 13. The display device of claim12, wherein the light emitting layer comprises a pattern of a quantumdot polymer composite.
 14. The display device of claim 13, wherein thepattern comprises a first repeating section configured to emit redlight, and wherein the first repeating section comprises the pluralityof the cadmium free quantum dots.
 15. The display device of claim 12,wherein the the light source comprises an organic light emitting diode.16. The display device of claim 15, wherein the organic light emittingdiode is configured to emit blue light, green light, or a combinationthereof.
 17. The display device of claim 12, wherein the display devicefurther comprises a substrate and an optical element, and the opticalelement is disposed between the substrate and the light emitting layer.18. The display device of claim 17, wherein the optical elementcomprises a layer that is configured to cut blue light and optionallygreen light.
 19. The display device of claim 12, wherein the displaydevice is configured to have color reproducibility of greater than orequal to about 80% measured in accordance with a BT2020 standard.